Many devices currently exist that are designed to track a laser or other type of electromagnetic source. For example, a laser guided projectile, such as a missile, may incorporate a laser guided seeker to accurately intercept or “strike” a selected target. A laser designator first illuminates the selected target, which then allows the laser guided seeker to detect the selected target by reflected laser “light” from the illuminated selected target. The laser guided seekers generally operate by using an avalanche photodiode detector or other type of light sensor to covert an optical wavelength, i.e. the reflected laser light, into an electrical signal.
A problem that often arises is that the laser guided seekers may detect and track an object other than the illuminated selected target. For example, because of the large field of view that most laser guided seekers have, solar background from the sun may confuse or disorient the light sensor, and the projectile may “lock in” on the sun. Thus, instead of the projectile directing itself towards the illuminated selected target, the projectile will direct itself towards the sun. Moreover, countermeasures may be deployed to similarly confuse the light sensor, such as a flame, fire, flare, or other type of heat (electromagnetic radiation) source. These countermeasures may cause the projectile to lock in on the countermeasure instead of the selected target. A system to focus a desired wavelength, such as the reflected laser light, and defocus background radiation, such as countermeasures or sun light, is desired.